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21.
The hydrosilylation of cyclohexanone and acetone with triethysilane and diphenysilane catalyzed by polymer‐supported Rh(I) complex has been investigated. Two terpolymers of styrene, divinylbenzene, and 1‐vinylimidazole (S/DVB/VI) or N‐vinylpyrrolidinone (S/DVB/NVP) were used as the catalysts supports. Physical characterization of these materials has involved the measurements of the structural parameters in the dry and swollen states by DSC, the nitrogen BET adsorption method and inverse steric exclusion chromatography ISEC. From these results it can be concluded that the original polymer structure has been changed during the complex attachment giving rise to materials of higher porosity. X‐ray photoelectron spectroscopy XPS, IR, and AAS spectroscopy were used to characterization of heterogeneous complexes before and after use. The effect of the morphology of the support on the catalytic properties of the polymer‐supported Rh(I) species was tested in the hydrosilylation of ketones and correlated with the reaction mechanism. It was demonstrated that the high selectivity of homogeneous rhodium complex toward the silyl ethers can be partially reversed to the dehydrogenative silylation products by a proper choice of polymer support with favorable microporous structure. Recycling tests demonstrated high stability of the supported catalysts during prolonged use. The constant selectivity of the supported catalysts demonstrated during recycling experiments showed that they could be useful for practical application. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 相似文献
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M. Aulice Scibioh In-Hwan Oh Tae-Hoon Lim Seong-Ahn Hong Heung Yong Ha 《Applied catalysis. B, Environmental》2008,77(3-4):373-385
High-performance fuel cell electrodes require architectures that offer appropriate electrochemical and nanoscopic catalytic reaction zones. In this direction, ionomer (perfluoro sulfonic acid)-coated carbon supports were prepared by adopting a simple and cheap synthetic strategy to offer both electronic and protonic contacts to the catalyst particulates. Pt–Ru bimetallic anode catalysts were prepared on these modified carbon supports by a colloidal method. The role of surface area of carbon supports and the influence of ionomer content in them towards the catalytic activities of Pt–Ru catalysts has been probed by using three kinds of carbon black powders with different physical properties. Their electrocatalytic efficiencies toward methanol oxidation were scrutinized via half-cell measurements in cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy. Catalysts particulates dispersed on carbon supports coated with ionomer exhibited better performance than those on the plain carbon supports, owing to the reduced micropores and increased interfacial area between catalyst particles and ionomer. Plain and modified carbon (MC) supports were characterized by using FTIR, BET-PSD and TEM techniques. Physico-chemical characterizations of supported catalyst systems were done by using XRD and TEM. 相似文献
26.
A dimethylsilylene‐bridged metallocene complex, (CH3)2Si(Ind)2ZrCl2, was supported on a nanosized silica particle, whose surface area was mostly external. The resulting catalyst was used to catalyze the polymerization of propylene to polypropylene. Under identical reaction conditions, a nanosized catalyst exhibited much better polymerization activity than a microsized catalyst. At the optimum polymerization temperature of 55°C, the former had 80% higher activity than the latter. In addition, the nanosized catalyst produced a polymer with a greater molecular weight, a narrower molecular weight distribution, and a higher melting point in comparison with the microsized catalyst. The nanosized catalyst's superiority was ascribed to the higher monomer concentration at its external active sites (which were free from internal diffusion resistance) and was also attributed to its much larger surface area. Electron microscopy results showed that the nanosized catalyst produced polymer particles of similar sizes and shapes, indicating that each nanosized catalyst particle had uniform polymerization activity. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
27.
Ebrahim Ahmadi Mehdi Nekoomanesh Haghighi Zahra Mohamadnia Ali Ramazani 《应用聚合物科学杂志》2010,118(6):3658-3665
Cr/SBA‐15 catalysts were prepared by the grafting of chromium nitrate nonahydrate [Cr(NO3)3·9H2O] complexes onto SBA‐15 mesoporous materials. Shish‐kebab and nanofiber polyethylenes (PEs) were prepared under different temperatures via ethylene extrusion polymerization with the Cr(NO3)3·9H2O catalytic system. The diameter of a single nanofiber was 100–250 nm. Scanning electron microscopy images showed that the polymer obtained from the SBA‐15‐supported catalyst under different polymerization temperatures produced nanofiber and/or shish‐kebab morphologies. X‐ray diffraction and differential scanning calorimetry were used to characterize microstructures of the materials. Polymers obtained with all of the catalysts showed a melting temperature, bulk density, and high load melt index; this indicated the formation of linear high‐density PE. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 相似文献
28.
A study about the performance of Pt(0.3 wt%)Sn(0.3 wt%) catalysts supported on different materials in n-butane dehydrogenation is reported in this paper. The materials used as supports were γ-Al2O3, ZnAl2O4 spinel, MgAl2O4 spinel and spheres of α-Al2O3 with a washcoating of γ-Al2O3. The syntheses of both spinels leaded to very pure ZnAl2O4 and MgAl2O4 supports. The material prepared by washcoating showed the presence of an uniform and homogeneous layer of γ-Al2O3 (with a thickness between 12 and 18 μm) deposited on the spheres of α-Al2O3.The best behavior in activity, selectivity and stability through five severe cycles was achieved by bimetallic PtSn catalysts supported on MgAl2O4 spinel and on the material prepared by washcoating. The very good performance of these catalysts through the different cycles of reaction-regeneration can be due to the presence of metallic phases which preserve the strong intermetallic interaction along the different treatments, thus avoiding segregation processes. 相似文献
29.
郭绍臣 《沈阳建筑工程学院学报(自然科学版)》1995,(4)
提出用力矩分配法计算弹性转动支座上的刚架,导出了弹性转动支座梁的形常数与载常数的计算公式,并附有例题. 相似文献
30.
In an earlier paper (Rozvany, Struct Optim 15:42–48, 1998), the second author summarized known analytical solutions for some popular benchmark problems in topology optimization. In
this, and in some subsequent papers, further exact optimal topologies are derived for least-weight, stress-controlled trusses,
with load and support conditions that are frequently used in benchmark examples for numerical methods in topology optimization. 相似文献